Door safety switch



Dec. 24, 1963 J. K. CAMPBELL 3,115,558

, DOOR SAFETY swrrca Filed Nov. 29. 1960 2 Sheets-Sheet 1 INVENTOR JOSEPH K. CAMPBEL L ATTORNEY Dec. 24, 1963 J. K. CAMPBELL DOOR SAFETY SWITCH Filed Nov. 29, 1960 2 Sheets-Sheet 2 m T m v w JOSEPH K. CAMPBELL 5r Q M ATTORNEY United States Patent Ofiice EJ115553 Patented Dec. 24, 1963 3,il5,55$ Diltlillt SWi'tllClll Joseph K. Campbell, East Earl, F39, assignor to Sperry Rand Corporation, New Holland, Pa, a corporation of Pennsylvania Filed Nov. 29, 196i Ser. No. 72,398 ll Claim. (tCl. 2M-6L5ti) This invention relates generally to safety devices and more particularly to a safety switch for a crop dryer to prevent the dryer from being operated when an access door is opened.

A conventional crop dryer has a cylindrical casing within which a high speed fan is located. An opening is provided in the side of the casing to make the fan accessible, as well as other structure within the casing. A door is provided to close such opening when the dryer is in use because any contact with the fan when it is in operation could cause very serious injury.

It is common to provide a switch operative responsive to closing of a door. For example, the light in a refrigerator is usually controlled by a switch having a plunger which is reciprocated when the refrigerator door is opened or closed. Such an arrangement is not suitable for a crop dryer because the plunger of the switch is readily accessible and can be manually operated. To provide such a switch in a dryer would enable an operator to open the dryer door and manually operate the switch to start the dryer fan. That would be dangerous and it is preferable to provide no means for allowing an operator to manually start the dryer fan when an access door is opened. Also, if an exposed switch is provided, it might "e inadvertently tripped by an operator and subject him to injury.

One object of this invention is to provide a crop dryer sa ety switch which requires that an access door in the dryer casing be closed before the dryer can be operated.

Another object of this invention is to provide a crop dryer safety switch which is incorporated into dryer structure including a door having a plurality of fastening members, one of the fasteners operating a normally opened safety switch and such fastening member having to be tightly in place before the switch is closed.

Another object of this invention is to provide a dryer safety switch which is inaccesible to the operator through the dryer casing opening when the access door is opened.

A further object of this invention is to provide a safety switch of the character described wherein a fastening member is projectable through a casing hole to operate a safety switch, the hole being so small that the operator is unable to insert a finger through the hole to trip the switch.

A still further object of this invention is to provide a safety device of the character described which is low in cost and utilizes presently existing and required structure.

in the drawings:

*lG. l is a fragmentary, part side elevation, part vertical section of a crop dryer having a safety switch constructed according to this invention;

PEG. 2 is an enlarged fragmentary section taken on the line 2-2 of FlG. 1 looking in the direction of the arrows;

3 is a section taken on the lines of FIG. 4 and showing the operative relationship of the safety switch and the closure door for the dryer; and

Phil. 4 is an enlarged fragmentary view looking from inside the dryer casing outwardly.

Referring now to the drawings by numerals of reference, ltl denotes a crop dryer having a forward cylindrical casing lll and a rear cylindrical casing 12. Casing ll contains a high speed electric motor 14 having an output shaft lie" to which a large fan 16 is connected. When the motor i i is operated, the fan 16 operates to blow air toward the left of FIG. 1. The motor lld is mounted within casing ii on support structure hi.

Heated air is produced by a burner unit and heat eX- changer indicated diagrammatically at 24} and 2-1, re spectively. Outside air is sucked into the dryer through opening 22 in casing 11 and forced through the casing 12 and over heat exchanger 21. The heated air blown from the unit may be directed to a crop to be dried.

Access to the fan in, burner unit 2t) and heat exchanger 21 is provided by a rectangular opening 25 in the side of easing section 12. Opening 25 is adapted to be closed by a removable door 26 having a tab 28 at its upper end which projects inside casing 12 and along the up er edge of opening 25 when the door is in place. The remainder of the door is somewhat larger than the opening 25 and overlies a portion of the side of the casing. T o fasten door 26 to the casing 115, wing screws 29 are provided. As shown best in FIG. 3, these wing screws proect through the door 26, through the side of casing 132 and thread into tapped fastening members 2? secured to the inside of casing 112. To remove the door 25, it is necessary to remove the fasteners 2%, and to insure that the fan motor will not be operating when the door 26 is not in place, a safety switch Sill is provided.

Safety switch comprises a inicroswitch 31 wired in circuit with tie motor Switch 31 has a plunger spring biased outwardly to a normal position wherein the circuit to the motor i is opened. The switch is carried on a support or shield located behind the wall of casing 12 and along the Vertical side edge 35 of the opening 25. Support 34 is laterally displaced relative to the opening 25, as best shown in FIGS. 2 and 4 but is closely adjacent thereto.

The support is connected to the casing lit by nuts and bolts Support 3d includes an inwardly extending side plate 3 8 which extends perpendicular to the side of casing 12 and prevents access to the switch 31 through the opening The support also includes a base po tion a top portion 39 which further limits access to switch Fill and prevents a person from inserting a hand through the opening 25 and manually operating the switch. Thus, when the switch 51 is connected to the inside of casing 11, it may not be manually operated.

To control switch Til, one of the wing screws which connects the door to casing 12 is utilized. Such wing screw, denoted it has a threaded shank 41, of desired length, which threads through a suitable tapped member 435 fastened to casing 12. The inner end of the shank d]; is engageable with the outer end of the plunger The parts are so designed and disposed relative to each other that when swing .crew it) is threaded through the door 2% and casing 12, it en ages plunger 32 and trips microswitch 3]. to close the circuit to the motor T he length of the shank ll. is such relative to the normal positon of the plunger 32 that wing screw has to be threaded substantially all the way in before the microswitch will be tripped. in like respect, the parts are so arranged that the first few turns of the wing screw dd to loosen it, releases the plunger 3-2 and shuts off the switch before the fastener is completely removed.

in dryers heretofore, switches have been provided to control the motor M. Likewise, access doors have been closed by fastening members. in the present invention, existing structure has been utilized to provide the safety arrangement, one of the door fasteners being utilized to control the safety switch for the dryer. Since the particular fastener which works the microswitch has to be threaded tightly before the switch will be actuated, it is necessary that the door be tightly in place before the dryer apparatus can be operated. Likewise, since the support structure 34 blocks off tl e switch from the top, bottom and one side, no access to the plunger 32 of the switch is permitted. Therefore, an operator is unable to remove the door 26 and manually trip switch 31 to operate fan 16. Likewise, since the switch is laterally spaced relative to the opening 25 and shielded, there is no danger of the switch being inadvertently tripped. Therefore, the operator is protected from possible injury by the fan 16. Also, the opening in the casing 12 through which shank 41 of the wing screw itl projects, is smaller than an adults finger so that a finger cannot be inserted through the casing to trip the switch.

While this invention has been described in connection with a particular embodiment thereof, it will be understood that it is capable of further modification and this application is intended to cover any variations, uses, or adaptations following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains, and as fall within the scope of the invention or the limits of the appended claim.

Having thus described my invention, what I claim is:

A circuit control safety structure comprising a casing having a wall provided with an access opening, a switch mounted inside said casing and laterally spaced from said opening, said switch including an element movable in a direction toward and away from said casing wall, said 4 switch element having a normal position spaced from said casing wall and a circuit including said switch being open, a door for closing said opening, fastening means for securing said door to said casing, said fastening means inciuding a fastening member projcctable through a hole in said casing and across said space to engage and move said switch element from said normal position and close said circuit, said hole being small whereby a person may not extend a finger through the hole to manually move the switch element to close said circuit, and a shield fixedly connected to said casing on the inside thereof, said shield having a side wall extending transverse to said casing and parallel to the direction of movement of said switch element, said side wall being located between said casing opening and said switch element and preventing access to the switch element through said opening when said door is removed.

References in the tile of this patent UNITED STAT S PATENTS 1,751,826 Marshall Mar. 25, 1930 2,156,572 Olby May 2, 1939 2,261,989 Gallup Nov. 11, 1941 2,725,437 Fields et a1 Nov. 29, 1955 2,798,136 TarboX July 2, 1957 2,855,582 Tweedale Oct. 7, 1958 

